1. Field of the Invention
The present invention relates to a dielectric recording apparatus, a dielectric reproducing apparatus, and a dielectric recording/reproducing apparatus for recording/reproducing information with high density in/from microdomains in a dielectric substance.
2. Description of the Related Art
As high-density, large-capacity recording/reproducing apparatuses of randomly accessible type, there are known an optical disc apparatus and a hard disc drive (HDD) apparatus. Moreover, a recording/reproducing technique using a scanning nonlinear dielectric microscopy (SNDM) for the nanoscale analysis of a dielectric (ferroelectric) material has been recently proposed by the inventors of the present invention.
In optical recording, which uses an optical pickup with a laser as a light source, data is recorded by forming pits that are concave-convex on a disc surface or forming a crystal phase or amorphous phase of a phase shift medium, and the data is reproduced by using the difference in the reflectance between the crystal phase and the amorphous phase or using the magneto optical effect. However, the pickup is relatively large, which is not appropriate for high-speed reading, and the size of the recording pit is defined by the diffraction limit of light, so that its recording density is limited to 50 G bit/inch2.
In the longitudinal recording of magnetic recording as represented by the HDD, a magnetic resistance (MR) head has been recently realized by using giant magnetic resistance (GMR), and its recording density is expected to be larger than that of the optical disc by using perpendicular magnetic recording. However, the recording density is limited to 1 T bit/inch2 because of thermal fluctuation of magnetic recording information and the presence of a Bloch wall in a portion in which a code is reversed. Even if patterned media are used considering the above cause, it is difficult to overcome this limit.
The SNDM can detect the plus and minus of a ferroelectric domain by measuring a non-linear dielectric constant of a ferroelectric material. The SNDM can perform the detection of the ferroelectric domain in sub-nanometer resolution by using an electrically conductive cantilever (or probe) provided with a small projection on its tip portion, which is used for an atomic force microscopy (AFM) or the like. In the SNDM, a resonance circuit is used for the detection of the ferroelectric domain. The resonance circuit is provided with a probe(s), an inductor, an oscillator and a return electrode. The oscillation in the resonance circuit generates a high frequency signal having a frequency determined by an inductance of the inductor and a capacitance of a ferroelectric material just under the tip portion of the probe. The high frequency signal is applied from the tip portion of the probe to the ferroelectric material and returns from the ferroelectric material to the resonance circuit through the return electrode placed near the tip portion of the probe. The differential capacitance of the ferroelectric material changes depending on the non-linear dielectric constant of the ferroelectric material. The resonance circuit converts the change of the differential capacitance into the change of the frequency of the high frequency signal. Namely, the resonance circuit performs frequency modulation. Then, frequency-amplitude conversion is performed on the frequency-modulated signal. Then, coherent detection is performed on the converted signal by using a lock-in amplifier or the like, so that information corresponding to the differential capacitance of the ferroelectric material is extracted. On the basis of the extracted information, the plus and minus of the ferroelectric domain is detected.
However, the SNDM is originally designed for an analysis apparatus. The SNDM has not been developed in view of a recording/reproducing apparatus. For example, in the SNDM analysis apparatus, a relatively low alternating current electric field is applied to the dielectric material, in order to convert the change of the differential capacitance of the dielectric material into the change of the frequency of the high frequency signal. Namely, this conversion is carried out in the situation that the alternating current electric field is being applied to the dielectric material. Because of this, an oscillator for generating the alternating current electric field is needed. As a result, it is difficult to reduce the size of the apparatus and the production cost of the apparatus. Furthermore, the rate of the data reproduction is restricted by the frequency of the alternating current electric field. The frequency of the alternating current electric field is relatively low. As a result, it is difficult to increase the rate of the data reproduction.